Japanese Patent No. 4689762 discloses an LED bulb as conventional LED light source devices of this type, which can include an optical system as illustrated in FIG. 1A.
The disclosed LED bulb can include an LED light emitting element 100 and a reflecting member 101 disposed forward of the LED light emitting element 100 in its light illumination direction. The reflecting member 101 can include a reflecting surface 105 facing to the light emission surface 102 of the LED light emitting element 100 and having a center axis 106. The reflecting surface 105 can be composed of an apex 103 projecting toward the light emission surface 102 of the LED light emitting element 100, and a curved conical reflecting surface 104 that is a side surface extending from the apex 103 and concavely curved toward the center axis 106.
With this configuration, the light emitted from the LED light emitting element 100 can be radially reflected sideward and obliquely rearward with respect to the light illumination direction by means of the curved conical reflecting surface 104 of the reflecting member 101. Then the curved conical reflecting surface 104 can form a pseud light source (E) by the reflected light (F) therefrom. According to the conventional light source device disclosed in the conventional art, the light emission direction of light from the pseud light source (E) can be substantially the same as the light emission direction of light from a halogen bulb with a filament. Consequently, the formed position and the size of the light emission region of the pseud light source (E) can be the same as those of such a halogen bulb.
In the LED bulb disclosed in Japanese Patent No. 4689762, the light from the pseud light source (E) can be reflected by the curved conical reflecting surface 104, so that the reflected light (D) can form the light distribution pattern 107 as illustrated in FIG. 1B with a curved conical shape projected by the curved conical reflecting surface 104. The light emitted from the pseud light source (E) can form distribution light characteristics and luminance distribution different from those of light emitted from a coiled filament with a constant diameter.
In other words, the light distribution characteristics of the pseud light source (E) can correspond to those of a coiled filament (F) that is prepared by winding filament while gradually changing the winding diameter to form a curved conical shape. Therefore, the pseud light source (E) can emit light rays including first light rays emitted from first portions corresponding to those of filament wound with larger diameters and second light rays emitted from second portions corresponding to those of filament wound with smaller diameters. When such a pseud light source (E) is mounted within a lighting fixture having a light distribution control system, the first light rays from the first portions of the pseud light source (E) can be controlled in light distribution characteristics in such a manner that they are spread by the light distribution control system while the second light rays from the second portions thereof can be controlled in light distribution characteristics in such a manner that they are converged to a certain direction.
As a result, the lighting fixture with such a pseud light source (E) installed therein is difficult to obtain the same or similar light distribution characteristics and illuminance distribution as or to those of a conventional lighting fixture including a coiled filament with a constant diameter. In short, even if a bulb is replaced with such an LED bulb, the light distribution characteristics of such a lighting fixture are remarkably different from those of a lighting fixture with a conventional bulb.
Furthermore, the reflecting member 101 having the curved conical reflecting surface 104 that can provide such a pseud light source (E) needs to be supported by a columnar support, and such a columnar support must be arranged in the vicinity of the reflecting member 101 due to the limited space within the lighting fixture. This, however, results in formation of a shadow by the columnar support shielding the light emitted from the pseud light source (E).